Image reading device

ABSTRACT

This invention provides an image reading device capable of precise detection of the optical signal over a wide wavelength range, by forming a photoelectric converting unit for converting the visible light into an electrical signal and a photoelectric converting unit for converting the invisible light into an electrical signal, in monolithic manner on a single semiconductor chip.

This is a division of application Ser. No. 08/944,418, filed Oct. 6,1997 now U.S. Pat. No. 6,094,281, which is a continuation of applicationSer. No. 08/174,453, filed Dec. 28, 1993, now abandoned, the disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading device adapted for usein an image information processing apparatus such as a facsimile, animage scanner, a copying machine or the like, and more particularly toan image reading device and a photoelectric converting element capableof converting optical signal not only of visible spectral region butalso of invisible spectral region into electrical signal.

2. Related Background Art

In the field of image reading device, there are already known acharge-coupled device (CCD), a MOS device and an amplifying deviceformed by connecting a capacitative load to the emitter of aphototransistor, as disclosed in the U.S. Pat. No. 4,791,469 granted tothe inventors T. Ohmi and N. Tanaka.

Also there are recently conceived various applications, and imagereading devices having novel functions are being required.

For example the copying machine is required, in addition to theimprovement in image quality and the color image reproduction, to havethe ability to recognize, reproduce and record an invisible image to thehuman eyes.

An example of such invisible image is the image formed with inkabsorbing infrared light.

In general, the sensor for detecting the invisible light is anindividual device, and requires a new design concept for effecting imagedetection, in combination with a sensor for detecting the visible light.

As a basic design concept, the present inventors already found atechnology of incorporating a sensor for visible light detection and asensor for invisible light detection in a single semiconductor chip.However, said technology still has a room for improvement.

On the other hand, the image quality improvement and the color copyingcapability of the copying machine has brought the danger of forgery ofbanknotes, stamps, valuable securities etc. into reality. For thisreason, in the recognition of banknote or the like, there have beendevised various methods such as detection of the stamp pattern on thebanknote.

Also utilizing the fact that the pattern of the original image is formedwith certain color hues, the present applicant already proposed a methodof recognizing the banknote etc. from the color hue of said originalpattern.

Also certain banknotes enable recognition of the true one and the falseone, by printing a predetermined mark with fluorescent ink which emitsvisible light when irradiated with ultraviolet light.

Also for forming such predetermined mark, tile use of ink capable ofabsorbing infrared light was also proposed by the present applicant.

In such infrared light detecting device, the Japanese Patent ApplicationLaid-open No. 4-286350 of which U.S. counterpart is U.S. Ser. No.139,174 entitled “Image Processing Apparatus and Method Therefore” filedon Oct. 21, 1993 proposing to achieve making compact of the device andeasy optical adjustment by a monolithic structure of a sensor forordinary color image formation and a sensor for infrared lightdetection, thereby enabling to use a common optical system.

However, such conventional system is difficult to design in common forplural valuable securities, because a visible pattern is the target ofrecognition. Therefore, for distinguishing the valuable securities of Nkinds, it has been necessary to select the features of N kinds inadvance and to independently recognize each security, and it has beendifficult to realize such apparatus inexpensively.

Also a CCD sensor for reading the images of visible and infrared regionsby separating the spectral regions additionally requires, in comparisonwith the conventional sensor, an optical filter for reading the infraredlight and an increased number of elements or lines of the sensor,whereby the sensor itself and the post-processing system therefor becomecomplex and a decrease in the light-receiving area of the sensor or anincrease in the size of the sensor is unavoidable.

Also, since the sensor elements for the visible light and those for theinfrared light are arranged on a same plane, at least one of the sensorsmay become out of focus, due to the difference in the focus position.

Also in case of using such sensors for respectively reading the infraredinformation and the visible information, it becomes necessary to clearlyseparate the visible information and other information.

Furthermore, for obtaining a satisfactory resolving power on amonolithic CCD sensor over a wide spectral range from visible tonear-infrared region or from visible to near-ultraviolet region, thereis required a significantly increased number of lenses, leading to anincreased cost and a larger space of the device. Also in an opticalsystem employing a short-focus lens array, it has been impossible tomaintain a constant resolving power over a wide spectral range, becausesuch lens array is composed of single lenses.

Also the conventional image reading device employed in the officeequipment such as copying machine is composed for example of a CCD or aMOS sensor requiring a long optical path, or a contact image sensoremploying amorphous silicon, and such image reading device is sometimescombined with color filters for the color image reproduction.

However, such photoelectric converting device combined with filters isnot necessarily superior, in terms of spectral sensitivity and resolvingpower for infrared light detection, to the device for visible lightdetection, and still has a room for improvement.

SUMMARY OF THE INVENTION

In consideration of the foregoing, the object of the present inventionis to provide a compact image reading device capable of detecting theoptical signal over a wide spectral range from visible to invisibleregion, and not giving much burden on the designing of the opticalsystem.

The above-mentioned object can be attained, according to an embodimentof the present invention, by an image reading device in which thelight-receiving face of a first sensor for converting the optical signalof the visible region into a first electrical signal and that of asecond sensor for converting the optical signal of the invisible regioninto a second electrical signal are provided in different positions withrespect to the incident direction of light.

According to another embodiment, there is provided an image readingdevice comprising reading means in which the light-receiving face of afirst sensor for converting the optical signal of the visible regioninto a first electrical signal and that of a second sensor forconverting the optical signal of the invisible region into a secondelectrical signal are provided in different positions with respect tothe incident direction of light, image forming means for forming animage based on said first electrical signal, discrimination means foreffecting discrimination based on said second electrical signal and areference signal, and control means for controlling the function of saidimage forming means based on the output of said discrimination means.

This embodiment enables highly precise image reading over a widespectral range, since the light-receiving face of the visible lightsensor and that of the invisible light sensor can be independentlypositioned at optimum conditions.

Still another embodiment of the present invention provides an imagereading device for secure recognition of a specified original image.

Still another embodiment of the present invention enables reading of theoriginal image in the visible light region and the infrared region,inexpensively and securely in a simple configuration.

The above-mentioned object can be attained, in said embodiments, by animage reading device provided with means for recognizing that an objectpixel is a specified image, based on the image information in thevisible region and that in the infrared region, in the position of theobject pixel and in the positions of the pixels in the vicinity, whereinthe image information of said visible region and infrared region areread by common use of a same image reading sensor or a part thereof, byswitching an optical filter for limiting the absolute light amount or aspecified spectral region.

Also there is provided an image reading device provided with means forrecognizing that an object pixel is a specified image, based on theimage information in the visible region and that in the infrared region,in the object pixel and in the pixels in the vicinity, comprising aswitchable optical distance correcting filter for correcting thedifference in the focus position between said visible region andinfrared region.

Still another embodiment of the present invention provides an imagereading device capable of satisfactorily reading the light of visibleregion and that of an invisible region.

The image reading device of this embodiment comprises a filter forintercepting the invisible light only between a sensor for reading thevisible information and the original image, in reading the visible andinvisible information by focusing on a solid-state image sensors formedin monolithic manner on a same substrate.

Also there is provided means for correcting the difference in focusposition between the visible and invisible information, in reading thevisible and invisible information by focusing on a solid-state imagesensors formed in monolithic manner on a same substrate.

Still another embodiment of the present invention provides aphotoelectric converting device improved in spectral sensitivity andresolving power.

According to this embodiment, there is provided a photoelectricconverting device for converting the optical signal of infrared regioninto an electrical signal, comprising a photoelectric converting elementfor converting the optical signal of visible region into an electricalsignal, and infrared-visible light conversion means for selectivelygenerating an optical signal of visible region to irradiate saidphotoelectric converting element, based on the optical signal ofinfrared region.

An electrical signal improved in spectral sensitivity and resolvingpower can be obtained by detecting the visible light generated accordingto the intensity or the presence or absence of the infrared light,instead of the conventional selective detection of the infrared lightwithin a wide spectral range covering from the visible to infraredregion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an embodiment 1-1 of theimage reading device of the present invention;

FIG. 2 is a chart showing spectral characteristics of color filters tobe employed in the present invention;

FIG. 3 is a chart showing spectral characteristics of a visible lightcut-off filter to be employed in the present invention;

FIG. 4 is a chart showing light emission characteristics of a lightsource to be employed in the present invention;

FIGS. 5A and 5B are schematic views of the embodiment 1-1 of the imagereading device of the present invention;

FIG. 6 is a schematic view of a pixel of the embodiment 1-1 of the imagereading device;

FIG. 7 is a chart showing spectral characteristics of infrared absorbingpaint to be employed in the present invention;

FIG. 8 is a chart showing spectral characteristics of a far-infraredcut-off filter to be employed in the present invention;

FIGS. 9A and 9B are schematic views of an embodiment 1-2 of the imagereading device of the present invention;

FIGS. 10A and 10B are schematic views of an embodiment 1-3 of the imagereading device of the present invention;

FIG. 11 is a schematic view showing an example of the image informationprocessing apparatus of the present invention;

FIG. 12 is a schematic view of an original image to be read by the imagereading device of the present invention;

FIG. 13 is a schematic view showing the reading operation of the imagereading device of the present invention;

FIG. 14 is a block diagram showing a signal processing unit of the imagereading device of the present invention;

FIG. 15 is a block diagram of an edge enchancing circuit of the imagereading device of the present invention;

FIG. 16 is a schematic view of a pixel data map;

FIG. 17 is a schematic view of a part of the original reading unit in anequal-size optical system in an embodiment 2-1;

FIG. 18 is a schematic view of a full-color copying machine in theembodiment 2-1;

FIG. 19 is a block diagram of the embodiment;

FIG. 20 is a flow chart of the control sequence of the embodiment;

FIGS. 21A and 21B are magnified views of the light-receiving elements ofthe CCD sensor in the embodiment 2-1;

FIG. 22 is a chart showing the spectral sensitivity characteristics ofthe CCD sensor in the embodiment;

FIG. 23 is a chart showing the spectral transmittance of thenear-infrared absorbing ink employed in said embodiment;

FIG. 24 is a chart showing the spectral characteristics of the originalilluminating lamp employed in the embodiment;

FIG. 25 is a chart showing the spectral characteristics of thefar-infrared cut-off filter employed in said embodiment;

FIG. 26 is a chart showing the spectral characteristics of the visiblecut-off filter employed in the embodiment;

FIG. 27 is a chart showing the spectral characteristics of the infraredcut-off filter employed in the embodiment;

FIG. 28 is a schematic view showing the vicinity of the lens and the CCDsensor in a reduction optical system in an embodiment 2-2;

FIG. 29 is a view showing the structure of a full-color copying machinein the embodiment 2-2;

FIG. 30 is a view showing the structure of the CCD sensor in theembodiment 2-2;

FIG. 31 is a schematic view showing the vicinity of the lens and the CCDsensor in a reduction optical system in an embodiment 2-3;

FIG. 32 is a view showing an example of the pattern in the embodiment;

FIG. 33 is a view showing the method for discriminating a specifiedoriginal in the embodiment;

FIG. 34 is a block diagram of the hardware realizing the discriminatingalgorithm of the embodiment;

FIG. 35 is a view showing the state of detecting the identification markof a copy-inhibited original, in an embodiment 3-1;

FIG. 36 is a view showing the structure of a color copying apparatusemploying the present invention;

FIG. 37 is a chart showing the spectral characteristics of the filterpositioned immediately after the original illuminating lamp in theembodiment;

FIG. 38 is a chart showing the spectral characteristics of the originalilluminating lamp employed in the embodiment;

FIGS. 39A and 39B are views showing the structure of the CCD sensoremployed in the embodiment;

FIG. 40 is a chart showing the spectral sensitivity characteristics ofthe CCD employed in the embodiment;

FIG. 41 is a chart showing the spectral characteristics of the infraredcut-off filter employed in the embodiment;

FIG. 42 is a chart showing the spectral characteristics of fluorescentlight in the embodiment;

FIG. 43 is an external view of the CCD sensor in an embodiment 3-2;

FIG. 44 is an external view of the CCD sensor in an embodiment 3-3;

FIG. 45 is a view showing the equal-size optical system in an embodiment3-4;

FIG. 46 is a view showing the structure of the CCD sensor employed inthe embodiment;

FIG. 47 is a chart showing the axial chromatic aberration of the readinglens;

FIG. 48 is a view showing the shape of the CCD cover glass employed inan embodiment 3-6;

FIG. 49 is an external view of the element for optical path splittingand optical length correction employed in the present invention;

FIG. 50 is a magnified view of the reading unit;

FIG. 51 is a chart showing the spectral characteristics of the element;

FIG. 52 is a view showing the structure of a color copying apparatus;

FIG. 53 is a chart showing the distance between the optical pathcorrecting mirror and the half mirror and the distance of separationbetween the visible and infrared lights as a function of the lightincident angle;

FIG. 54 is a chart showing the spectral characteristics of the dichroicmirror;

FIG. 55 is a schematic cross-sectional view of an example of thephotoelectric converting device of the present invention;

FIG. 56 is a schematic cross-sectional view of another example of thephotoelectric converting device of the present invention;

FIG. 57 is a spectral chart showing the infrared exhausting effect; and

FIG. 58 is a schematic cross-sectional view of the photoelectricconverting device of the present invention, utilizing the infraredexhausting effect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The image reading device of the present invention is featured by a factthat the light-receiving face of the sensor for visible light and thatof the sensor for invisible light are made respectively different forthe direction of the incident light, but the planar positions (positionsin a plane perpendicular to the incident direction) of said sensors arenot particularly limited. However, in case of a line sensor, the sensorarray for visible light and that for invisible light are preferablyconstructed as separate lines. Also in the sensor array for visiblelight, the sensor elements for red (R), green (G) and blue (B) or thesensor elements for yellow (Y), cyan (C) and magenta (M) may bepositioned in an in-line arrangement or may be arranged to constitutethree parallel lines.

FIG. 1 is a schematic cross-sectional view of the image reading deviceof the present invention, wherein a sensor 2 for visible light has alight-receiving face 2′ which is different from that 3′ of a sensor 3for invisible light.

The photoelectric converting elements (sensor elements) constituting thelight-receiving face of the present invention are advantageouslycomposed of photo-voltaic elements or photoconductive elements such asphotodiodes or phototransistors. The photoelectric converting elementsfor converting the optical signal of the visible region into theelectric signal may be constituted by the elements composed of amaterial capable of selectively absorbing the optical signal of thevisible region only, or by the elements provided with a filter capableof transmitting the light of visible region but intercepting the lightof a spectral region to be utilized for photoelectric conversion inother photoelectric converting elements, among the invisible region.

More specifically, for obtaining a black-and-white signal, there isattained selective sensitivity in the visible wavelength region from 400to 700 nm, by selecting the material constituting said elements or byproviding the elements with a filter selectively transmitting the lightof the above-mentioned wavelength region. Also the optical signal of aspecified region within the visible spectral region may be obtained byconstructing said elements with a material selectively havingsensitivity in said specified region, or by providing the elements witha filter capable of transmitting the light of said specified spectralregion.

Also for obtaining color signals, such as of red (R), green (G) and blue(B), there are employed elements of plural kinds, consisting of elements(R elements) having selective sensitivity in the R region (spectralregion for example from 580 to 700 nm), elements (G elements) havingselective sensitivity in the G region (spectral region for example from480 to 580 nm), and elements (B elements) having selective sensitivityin the B region (spectral region for example from 400 to 480 nm).

Also in this case, there may be employed elements composed of materialshaving selective sensitivities in, namely capable of selectivelyabsorbing the lights of the above-mentioned R, G and B regions, orprovided elements having sensitivity in all the R, G and B regions withfilters selectively transmitting the lights of said R, G and B regionsrespectively.

Alternatively, a position of a semiconductor junction such as a PNjunction of the photodiode or the phototransistor may be varied toobtain a selective sensitivity.

FIG. 2 is a chart showing the representative spectral characteristics ofthe light transmitted by the filters, wherein the relative sensitivityin the ordinate corresponds to the transmittance for the visible light.In case the elements are given the selective sensitivities by theselection of the constituting materials, the elements are formed withthe materials having the light absorbing characteristics correspondingto the relative sensitivities shown in FIG. 2.

In the present invention, any of the visible and invisible spectralregions, and the R, G and B spectral regions are not clearlydistinguished by the wavelength, but the photoelectric convertingelements to be employed therein need only to be so constructed as tophotoelectrically convert the ultraviolet, blue, green, red and/orinfrared lights by a necessary amount and substantially not to convertthe unnecessary lights, in order to obtain the required signals.

On the other hand, for converting the optical signal of the invisiblespectral region into the electrical signal, there are employedphotoelectric converting elements having selective sensitivity forexample for the ultraviolet light or the infrared light. Also in thiscase there may be employed elements composed of a material havingselective sensitivity in said invisible spectral region, or elementscomposed of a material having sensitivity in a wide spectral rangeincluding said invisible spectral region, composed with a filter havingselective transmittance for the light of said invisible spectral region.

FIG. 3 is a chart showing representative spectral characteristics of theabove-mentioned filter, wherein the relative sensitivity in the ordinatecorresponds to the transmittance for the invisible light. There is shownan example of filter having selective sensitivity in the infrared region(wavelength region for example above 750 nm), but such example is notlimitative.

The solid-state image reading device of the present invention may beconstructed as a color line sensor as shown in FIG. 1, in which theelements for visible light and those for invisible light areperiodically arranged in mutually separate lines. Preferably it is soconstructed that a pixel in terms of the resolving power of the colorsignal contains an element (R element) having selective sensitivity inthe R region, an element (G element) having selective sensitivity in theG region, an element (B element) having selective sensitivity in the Bregion, and an element (IR element) having selective sensitivity in theinvisible region.

The optical signal to be detected may be generated from athree-dimensional image or a two-dimensional image, and a representativeexample of said two-dimensional image is a flat image such as anoriginal document. Consequently, in case of use in a system for readingthe image of an original document, there is preferably providedillumination means for illuminating the original. Such illuminationmeans may be composed for example of a light-emitting diode, a xenonlamp or a halogen lamp. FIG. 4 shows representative light emissionspectral characteristics of the light source. However the light sourceneeds only to emit the light of a spectral region required correspondingto the optical signal to be detected, and is not limited to that havingthe characteristics shown in FIG. 4. A light source emitting the lightof the characteristics shown in FIG. 4 can at least provide the light inthe R, G and B regions and the infrared light in the invisible spectralregion.

In the following there will be explained embodiments of the presentinvention, but it is to be understood that the present invention is notlimited to these embodiments but can be realized in any form attainingthe objects of the present invention.

(Embodiment 1-1)

FIG. 5A is a plan view, seen from above, of a CCD 1 serving as the imagereading device, and FIG. 5B is a cross-sectional view thereof.

The CCD 1 is composed of a first element array 100 and a second elementarray 101.

In the first element array 100, the elements are cyclically providedwith R filters 102, G filters 103, and B filters 104, formed byevaporation, in the order of R, G, B, R, G, B, . . . therebyconstituting a reading system in which a pixel 105, consisting of a setof three elements of R, G and B, constitutes a minimum reading area.

The filters provided by evaporation on respective elements have thespectral characteristics as shown in FIG. 2.

On the other hand, in the second element array 101, the elements arearranged with a pitch equal to three times of the pitch of the elementsin the first element array 100. Stated differently, the element pitch ofthe second array 101 is same as the pixel pitch of the first elementarray 100.

The second element array 101 is provided, by evaporation, with a visiblelight cut-off filter of the characteristics shown in FIG. 3, so that thelight components less than 700 nm are cut off and the element array 101can read the infrared component.

Also, as shown in FIG. 5B, the second element array 101 has a stepdifference d of 300 μm to the first element array 100, for obtaining alonger optical path. This is because the focal length of the opticalsystem varies depending on the wavelength, and the image becomes out offocus for the infrared light unless the optical path is made longer.

FIG. 6 shows the dimension and the positional relationship of theelements of the first element array 100 and the second element array101. It is assumed that the reading unit has a resolving power of 400dpi and that, for the purpose of simplicity, an equal-size opticalsystem is employed.

For realizing the resolving power of 400 dpi, the minimum reading areabecomes 63.5×63.5 μm. Consequently the size of the R, G and B elementsbecomes 21.1×63.5 μm, while the IR elements becomes 63.5×3.5 μm. Thedistance between the first and second element arrays is selected as 127μm. Stated differently, said arrays are separated by a distancecorresponding to twice of the array 100 or 101.

The signals read by the arrays 100, 101 are so controlled as to betransmitted to a signal processing unit 211.

(Embodiment 1-2)

In this embodiment, the element array 101 can read the signal in aspectral region exceeding 700 nm, but the infrared absorbing paint has aspectral distribution having an extremely narrow band width, with a peakat 800 nm, as shown in FIG. 7.

However, depending on the light source to be employed, there may beprovided enough energy even in a region exceeding 1000 nm.

If such light source is employed, the discrimination of absorptionbecomes difficult because of the unnecessary energy above 800 nm. Forthis reason, the element array 101 is preferably provided with a farinfrared cut-off filter of the characteristics as shown in FIG. 8.

Said far infrared cut-off filter may be provided in any position in theoptical path, because, in the element array 100, the far infrared lightis already cut off by a filter evaporated on the surface of theelements.

For example, said filter may be conveniently positioned in front of orbehind a lens 209, because the filter can be easily replaced when thefluorescent characteristics of the fluorescent paint to be printed onthe original document is varied.

(Embodiment 1-3)

In the foregoing embodiments, the color sensor is constructed as shownin FIGS. 5A and 5B. In the present embodiment, the substrate of the CCDis formed in an inclined shape as shown in FIGS. 9A and 9B, in such amanner that the first line 100 and the second line 101 has a opticalpath difference d of 300 μm.

In this manner the visible optical signal and the infrared opticalsignal are both in focus, so that the precision of discriminationbecomes improved.

Also as a variation of this embodiment, a similar effect can be obtainedby placing planar CCD sensors in an inclined position.

(Embodiment 1-4)

In this embodiment, a color sensor consisting of an array 171 havingsensitivity to blue, an array 172 having sensitivity to green, an array173 having sensitivity to red and an array 174 having sensitivity toinfrared region is given step differences, matching the focal positionsof respective colors. There are preferably provided a step difference d1of 20 μm between B and G, a step difference d2 of 50 μm between G and R,and a step difference d3 of 280 μm between R and IR.

These values depend on the optical system to be employed, and arepreferably optimized according to each optical system.

The presence of four CCD lines requires phase matching of all the colorsignals with a FIFO memory.

Also as modifications of this embodiment, it is possible to form thesubstrate in inclined manner or to place a planar sensor in inclinedmanner.

In this manner the visible optical signal and the infrared opticalsignal are both in focus, so that the precision of discrimination can beimproved.

Also the distance between the array of the infrared component readingelements and the array of the visible component reading elements,selected as an integral multiple of the resolving power of the readingsystem, enables electrical compensation of said difference for exampleby a line buffer, and facilitates comparison of the signals from the twoelement arrays which read a same image area. It is furthermore possibleto dispense with said line buffer, by utilizing the FIFO memory forexample in an edge enhancing circuit.

(Image Information Processing Apparatus)

In the following there will be explained a representative example of theimage information processing apparatus equipped with the image readingdevice, according to any of the foregoing embodiments of the presentinvention.

(Structure of Image Scanner Unit)

In FIG. 11 there are shown an image scanner unit 201 for reading theoriginal image and effecting digital signal processing, and a printerunit 202 for printing a full-color image on a sheet, corresponding tothe original image read by the image scanner unit 201.

In the image scanner unit 201, there is provided a mirror-surface thickplate 200. An original 204 placed on an original supporting glass(hereinafter called platen) 203 is illuminated by a halogen lamp 205,and the reflected light from the original is focused, by a lens 209, onsaid color sensor 1 serving as the image reading device, whereby thefull-color signals of the red (R), green (G), blue (B) and infrared (IR)components are supplied to a signal processing unit 211.

A reading unit 207 is mechanically moved, with a velocity v, in aperpendicular direction (hereinafter called sub scanning direction) tothe electrical scanning direction (hereinafter called main scanningdirection) of the color sensor, thereby scanning the entire surface ofthe original.

The signal processing unit 211 electrically processes the read signalsto separate the components of magenta (M), cyan (C), yellow (Y) andblack (BK), for supply to the printer unit 202.

(Structure of the Printer Unit)

The image signals M, C, Y, BK supplied from the image scanner unit 210are supplied to a laser driver 212, which in response modulates asemiconductor laser 213. The laser beam emitted therefrom is guidedthrough a polygon mirror 214, an f-θ lens 215 and a mirror 216 and scansa photosensitive drum 217.

A rotary developing unit 218 is composed of a magenta developing unit219, a cyan developing unit 220, a yellow developing unit 221 and ablack developing unit 222, which in turn come into contact with thephotosensitive drum to develop the electrostatic latent images of M, C,Y and BK formed on the photosensitive drum 217 with correspondingtoners.

A sheet supplied from a sheet cassette 224 or 225 is wound on a transferdrum 223, and the toner images developed on the photosensitive drum 217are transferred onto said sheet.

After the successive transfers of the four color images of M, C, Y andBK in this manner, the sheet is discharged through a fixing unit 226.

In the foregoing there has been briefly explained the structure of thescanner unit and the printer unit principally constituting theapparatus, and in the following there will be given a detailedexplanation on the image scanner unit 201.

(Original)

FIG. 12 shows an original 630 on which a pre-registered pattern 631 isprinted with infrared absorbing paint.

In addition to the pattern 631, characters and images 632 are printedwith ordinary ink on the original 630.

The printed infrared absorbing paint, absorbing the infrared lighthaving wavelength in excess of 700 nm, appears almost colorless to thehuman eyes sensitive to a spectral region of 400-700 nm, and istherefore extremely difficult to recognize.

The spectral characteristics of said infrared absorbing paint is same asshown in FIG. 7.

The amount of the above-mentioned infrared absorption can be detected bycutting off the visible light component and extracting the infraredlight component only by the element array 101 in the sensor 1.

(Pre-scan)

The image scanner unit 201 effects a pre-scan, as a pre-treatment beforethe copying of the original 630, as will be explained in the following.

At first the lamp 205 illuminates a white shading plate 640, fixed in apart of the platen 203 as shown in FIG. 13.

The reflected image of said white shading plate 640 is focused, throughthe lens 209, onto the CCD 210.

The image of the white shading plate 640, read by the element arrays100, 101 of the sensor 1, is processed in the signal processing unit211, and the data for compensating the unevenness in the illumination bythe lamp 205, and the data for compensating the unevenness in thesensitivity of the element arrays 100, 101 of the sensor 1 are preparedand are stored for respective arrays.

Subsequently the reading unit 207 is mechanically moved in a direction mwith a velocity v by an unrepresented driving system, thereby scanningthe entire surface of the original. In this operation, the signalprocessing unit 211 extracts the maximum and minimum values of theoriginal density, from the image of the original 630 read by the elementarray 100 of the sensor 1, and calculates the print density at thecopying operation.

Thereafter the reading unit 207 is mechanically moved in a direction nshown in FIG. 13 with a velocity v by the unrepresented driving system,for returning to the reading start position, or, the home position.

(Copying of Original and Pattern Detection)

After the preparation of the above-mentioned shading correction data,the reading unit 207 returns to the home position and starts the readingof the original 630. At the same time there is detected whether theoriginal 630 has the pattern 631.

The presence or absence of the pattern is discriminated by thecomparison of the information read by the element array 100 of thesensor 1 and that read by the element array 101.

More specifically, the image reading for image reproduction is conductedby the element array 100, while the image reading for detecting thepattern 631 is conducted by the element array 101.

In the following there will be given an explanation on the signalprocessing unit 211 for processing the read signals. The block diagramof said unit 211 is shown in FIG. 14.

At first there will be explained the signal processing system for theelement array 100.

The analog image signals released from the element array 100 areentered, in the order of R, G and B and in synchronization with thedrive signal for the sensor 1, simultaneously to three sample-holdcircuits 121 a-121 c. The sample hold circuit 121 a generates a samplingsignal at the timing of entry of the R signal, and is capable ofretaining the analog level of the sampled signal until a next R signalis entered.

Similarly the sample-hold circuit 121 b generates a sampling signal atthe timing of entry of the G signal and the sample-hold circuit 121 cgenerates a sampling signal at the timing of entry of the B signal.

As a result, the sample-hold circuits 121 a-121 c respectively releasethe R, G and B signals, which are respectively supplied to A/Dconverters 122 a-122 c, wherein the analog image signal is convertedinto an 8-bit digital image signal. The obtained digital signals aresupplied to shading correction circuits 124 a-124 c, for being subjectedto shading correction.

The shading correction has already been explained in relation to thepre-scanning, and the correction data for R, G and B colors preparedtherein are stored in a RAM 123.

During the image reading, the correction data for each element aresupplied from the RAM 123 to the shading correction circuits 124 a-124c, thereby correcting the read data.

The image signals released from the shading correction circuits 124a-124 c are supplied to a 5×5 edge enhancing circuit 125, whichemphasizes the contour of the read image in the following manner.

FIG. 15 shows the structure of said edge enhancing circuit 125. The edgeenhancement is conducted for each of the R, G and B colors, but FIG. 15shows the circuit for one color only. Naturally other two circuits havethe identical structure.

In FIG. 15 there are provided FIFO memories 131-134 each having acapacity capable of retaining the data of a line in the element array100 of the CCD 210.

The four FIFO memories are connected as shown in FIG. 15, so that, whenthe pixel data of an n-th line are entered to the FIFO 131, the FIFOmemories 131, 132, 133, 134 respectively release the data of an (n−1)-thline, an (n−2)-th line, an (n−3)-th line and an (n−4)-th line.

The input signal and the output signals of the FIFO memories 131-134 aresupplied to a delay circuit 135.

Said delay circuit 135 is provided with several pixel delaying circuitsfor the entered signal of m-th pixel, thereby providing an arithmeticoperation circuit 136 with the pixel data of the (m−1)-th, (m−2)-th,(m−3)-th and (m−4)-th pixel as well as the m-th pixel. Thus the circuit136 receives the data of 25 pixels in total.

FIG. 16 shows the map of the entered data. Thus the operation unit 136receives the data of the surrounding 24 pixels together with the data ofa hatched object pixel.

The operation unit 136 multiplies the data of the object pixel by 25,and subtracts the data of the surrounding pixels.

Thus, if the data of the object pixel is larger than the data of thesurrounding pixels, the data of the object pixel becomes even larger,and vice versa.

This process increases the contrast of the contour of the image, thusenhancing the reproduced image.

The edge enhanced image data are supplied, through a logarithmicconversion unit 127 for effecting luminance-density conversion, and amasking conversion unit 128 for effecting optimum correlated colorcorrection, to the printer unit.

In the following there will be explained the signal processing systemfor the element array 101. Although it is basically same as that for theelement array 100, but the edge enhancing circuit is eliminated becausethe image reproduction is not the object.

The data released from a shading correction circuit 124 d are suppliedto a signal comparison circuit 126.

Other input data are obtained from the edge enhancing circuit, but, aswill be apparent from FIG. 6, the object pixel in the edge enhancingcircuit is present on the (n−2)-th line.

The comparison of the data of the arrays 100, 101 would require a linebuffer for compensating the distance of two lines as shown in FIG. 6,but the edge enhancement on the data of the array 100 provides the datacorresponding to a same position on the original. The signal comparisoncircuit 126, serving as the discrimination means, compares the imagedata of the arrays 100, 101 and sends the result of comparison to anunrepresented CPU.

In the signal comparison, it is to be noted that the printing ink of ahigh density and a low saturation tends to contain pigment of carbonblack family, and such ink, absorbing the infrared light, has to beseparated from the information to be discriminated.

In the present embodiment, therefore, whether the IR absorption patterncorresponds to the pattern to be discriminated is identified by thecomparison of the minimum value K of the R, G and B signals and the IRsignal in the following manner:

X=IR−const.×min(R, G, B).

More specifically, the value X is determined for each pixel and iscumulatively added for the entire original, and when the cumulativevalue reaches a predetermined reference level, the unrepresented CPUfunctions as the control means for the image forming operation andcontrols the printer unit so as to immediately interrupt the copying ofthe original.

There can be conceived certain variations in the image informationprocessing apparatus explained above.

For example the line position correction for the element arrays 100, 101need not necessarily utilize the FIFO memories of the 5×5 edge enhancingcircuit, but may instead utilize the FIFO memories for example of theerror diffusion process.

Also the pattern discrimination is not necessarily limited to the signalcomparison in the signal comparison circuit but may rely on patternmatching according to the image shape extracted by the signalcomparison, in order to control the original copying operation. In thiscase there is required a large and complex pattern matching circuit,but, as the kind of the original can be identified from the patternshape, there is enabled such control as to authorize the copyingoperation for certain originals in response to the entry of a password,but to prohibit the copying operation for other originals.

This embodiment enables precise detection of the optical signal with awide dynamic range and over a wide spectral range, without complicatingthe optical system.

(Embodiment 2-1)

The following embodiment shows an application of the present inventionto a copying apparatus, but such application is not limitative and thepresent invention is naturally applicable to various other apparatus,such as an image scanner connected to a computer.

FIG. 18 shows the structure of an embodiment 2-1 of the device of thepresent invention, wherein an image scanner unit 1101 effects originalreading and digital signal processing, and a printer unit 1202 forprinting a full-color image on a sheet, corresponding to the originalimage read by the image scanner unit 1101.

(Image Scanner Unit)

FIG. 17 is a schematic view showing a part of the original reading unitof the equal-size optical system of said image scanner unit 1101,provided with a mirror-surface pressure plate 1100. An original document1104 placed on an original supporting glass (hereinafter called platen)1103 is illuminated by a halogen lamp 1125, of which spectralcharacteristics are shown in FIG. 24, and the reflected light from theoriginal is supplied to a lens array 1122 and is subjected to thecut-off of a spectral region above about 850 nm by a dichroic filter1130 of which the spectral characteristics are shown in FIG. 25. Then bymeans of switchable filter means provided on a horizontally movablestage 1128, the image of the near-infrared region around a wavelength of800 nm or the image of the visible spectral region of 400-700 nm isselectively supplied to a CCD line sensor for image reading. Said stage1128 is driven by a laminated piezoelectric actuator 1129 andselectively moves in the lateral direction in FIG. 17. On said stage1128 there are mounted a filter 1123 of which the spectralcharacteristics are shown in FIG. 26, and a near-infrared cut-off filter1124 of which the spectral characteristics are shown in FIG. 11, andsaid stage 1128 is so moved that the filter 1123 or 1124 is insertedbetween the lens array 1122 and the sensor 1121 respectively at theimage reading in the near-infrared region or that in the visible region.On said filter 1124 there is provided a glass plate 1127 forcompensating the difference in image positions between the near-infraredlight and the visible light in this embodiment 2-1.

FIGS. 21A and 21B show the structure of the sensor 1121 employed in thepresent embodiment.

The sensor 1121 is composed of a single photosensor element array, inwhich the photosensor elements are provided with evaporated filters ofR, G and B colors which are cyclically arranged in the order of R, G, B,R, G, B . . . thereby constituting a reading system in which a pixelconsisting of a set of R, G and B photosensor elements is the minimumreading area. The spectral characteristics of said filters are shown inFIG. 22. The elements equipped with the R filter are sensitive also tothe invisible spectral region above 700 nm, and are capable ofsatisfactory image reading in the near-infrared region around 800 nm, bythe use of the filter 1123 and the dichroic filter 1130. For thephotosensor elements having the G or B filter the relative sensitivityabove 700 nm is not shown, because the data from said photosensorelements are used only for the image reading in the visible region. Infact the relative sensitivity above 700 m can be considered as almostzero in the image reading in the visible region, because theaforementioned near-infrared cut-off filter 1124 is used in the imagereading in the visible region.

In order to realize a resolving power of 400 DPI (dots per inch) withthis sensor, the minimum reading area should be of a size of 63.5×63.5μm. Consequently, the R element 152, G element 153 and B element 154should be of a size of 21.1×63.5 μm each. Also the image reading in theIR region utilizes the R elements, so that the reading area becomes21.1×63.5 μm.

The image data focused on the sensor 1121 are supplied, in the form ofthe red (R), green (G) and blue (B) components of the color information,to a signal processing unit 1198. The original scanning unit 1111 ismechanically moved with a velocity V, in the perpendicular direction(hereinafter called sub scanning direction) to the electrical scanningdirection (hereinafter called main scanning direction) of the linesensor, thereby scanning the entire area of the original.

A standard white board 1199, positioned to be illuminated by saidoriginal illuminating means when it is in a reference position(hereinafter called home position) and positioned at an optical distancesame as the distance from the sensor to the original on the platen,serves to correct the unevenness in the image data read by the sensor1121 when the halogen lamp 1125 is used. More specifically, the dataobtained from said white board are used as the correction data in theknown shading correction.

The signal processing unit 1198 electrically processes the read R, G andB signals to separate said signals into the components of magenta (M),cyan (C), yellow (Y) and black (BK) for supply to the printer unit 1202.In an original scanning operation of the image scanner unit 1101, one ofthe above-mentioned components M, C, Y and BK is supplied to the printerunit 1202, so that a printout is completed by four original scanningoperations in total.

(Printer Unit)

The M, C, Y and BK image signals supplied from the image scanner unit1101 are sent to a laser driver 1212, which modulates a semiconductorlaser 1213 according to the image signal. The emitted laser beam isguided through a polygon mirror 1214, an f-θ lens 1215 and a mirror 1216and scans a photosensitive drum 1217.

A magenta developing unit 1219, a cyan developing unit 1220, a yellowdeveloping unit 1221 and a black developing unit 1222 are brought inturn into contact, by means of an unrepresented sliding mechanism, withthe photosensitive drum 1217 to develop the electrostatic latent imagesof M, C, Y and BK colors formed on thereon with toners of correspondingcolors.

A sheet supplied from a sheet cassette 1224 is wound on a transfer drum1223 and the toner images developed on the photosensitive drum 1217 aretransferred onto said sheet.

After the successive transfers of four color images of M, C, Y and BK inthis manner, the sheet is discharged through a fixing unit 1226.

(Original Scanning)

In the following the original scanning sequence in the presentembodiment will be explained with reference to a flow chart shown inFIG. 26. When the original is set on the platen 1103 and a start buttonof the full color copying apparatus shown in FIG. 28 is depressed, theaforementioned movable stable 1128 is moved to the right in FIG. 17 andis set in a state for reading the image in the near-infrared region(S1). In this state there are conducted the fetching 20 of the shadingcorrection data (S2) and the first pre-scanning (S3) and the image dataof the near-infrared region, read by the sensor elements with the Rfilter with a density of 400 DPI both in the main and sub scanningdirections, are subjected to A/D conversion into 8-bit digital signalsand are stored in a memory (DRAM) 1161 shown in FIG. 19 (S4).Subsequently said movable stage is moved to the left and is set in astate for ordinary image reading in the visible region (S5), and, inthis state, there are conducted the fetching of the known shadingcorrection data (S6) and the second pre-scanning (S7). The image data,obtained in color separated state by the sensor elements having the R, Gand B filters with a density of 400 DPI both in the main and subscanning directions, are subjected to A/D conversion into 8-bit digitalsignals and are supplied to a discrimination unit 1163, together withthe image data of the near-infrared region stored in the above-mentionedmemory 1161 (S8). If the original is not identified as a specifiedoriginal by said discrimination unit (S9), the original scanningoperation is repeated four times for releasing the aforementioned M, C,Y and BK signals (S10). At the same time the image processing unit 1162effects image processings such as the variation of the imagemagnification, masking, undercolor removal etc. and the image signal ofone of M, C, Y and BK colors is supplied to the printer unit at eachscanning operation (S11).

If the discrimination unit 1163 identifies a specified original (S9),the ordinary image reading operation is suspended. Otherwise therecording control unit 1164 prohibits the faithful image reproduction,for example by painting the entire image with a particular color, or bymodifying the recording signal.

(Original Discrimination)

In the following there will be briefly explained the image pattern to bedetected in the present invention, with reference to FIGS. 23 and 32.

The transparent ink shown in FIG. 23 has the spectral characteristics ofa transparent dye substantially transmitting the light of the visibleregion but absorbing the infrared light around 800 nm. A representativeexample of such dye is SIR-159 supplied by Mitsui Toatsu Chemical Co.,Ltd.

FIG. 32 shows an example of the pattern formed by the transparent inkcontaining the above-mentioned transparent infrared-absorbing dye. On atriangular pattern recorded with ink reflecting the specified infraredlight, a small square pattern b with a side of about 120 μm is printedwith said transparent ink.

Said pattern b, being of almost same color as that of the triangularpattern in the visible region, is unrecognizable to the human eyes, butis detectable in the infrared region. Said pattern of ca. 120 μm, whenread with a density of 400 DPI, corresponds to the size of about 4pixels, as shown in FIG. 32. In the following there will be explainedthe details of the discrimination unit 1163 shown in FIG. 19, withreference to FIG. 15 wherein provided are FIFO memories 131-135 eachhaving a capacity capable of retaining the data of a line of the 1121.

The four FIFO memories are mutually connected as shown in FIG. 15, sothat, when the pixel data of an n-th line are entered into the FIFOmemory 131, the FIFO memories 131, 132, 133, 134 respectively releasethe data of an (n−1)-th line, an (n−2)-th line, an (n−3)-th line and an(n−4)-th line. The input signal and the output signals of the FIFOmemories 131-134 are supplied to a delay circuit 135, which has severalpixel delay circuits for the entered m-th pixel signal, therebysupplying an operation circuit 136 with the data of the (m−1)-th,(m−2)-th, (m−3)-th and (m−4)-th as well as the m-th pixel. Consequentlythe operation circuit 136 receives the data of 25 pixels in total. Themap of the entered data is shown in FIG. 33. With respect to the objectpixel position X, four pixels A, B, C and D are positioned as shown inFIG. 33. Therefore, if the object pixel X is reading the pattern b inFIG. 32, the pixels A, B, C and D are reading the image of the pattern apositioned therearound.

(Discrimination Algorithm)

Let us assume that the signal of the pixel A is composed of an Rcomponent A_(R), a G component A_(G), a B component A_(B) and an IRcomponent A_(IR), and likewise for the pixels B, C and D. The averagesY_(R), Y_(G), Y_(B) and Y_(IR) of the same color component in thesignals of the pixels A, B, C and D are determined by the followingequation:

Y _(K)=¼(A _(K) +B _(K) +C _(K) +D _(K)) (K=R, G, B, IR)

The discrimination of the object pattern is made according to thedifference between the average Y_(K) determined in the foregoingequation and the object pixel X. More specifically, the object patternis discriminated as present when the next relation stands:

ΔK=|Y _(K) −X _(K)|(K=R, G, B, IR)

wherein:

(ΔR<H)∩(ΔG<H)∩(ΔB<H)∩(ΔI R>J) (H, J: constant)

In this situation, in comparison with the surrounding pixels, the objectpixel is little different in the color hue in the visible region and hasa difference exceeding a constant L in the infrared region. FIG. 34shows an example of the hardware realizing the discrimination algorithmexplained above.

Adders 1081 respectively add the components of four pixels and releaseupper 8 bits to obtain Y_(R)Y_(G), Y_(B) and Y_(IR), respectively.Subtractors 1082 calculate the differences from the components of thesignal of the object pixel. For three components R, G and B, theabsolute values of said differences are respectively compared with theconstant H in comparators 1083, 1084 and 1085. On the other hand, theinfrared component is compared with the constant J in a comparator 1086.The outputs of the above-mentioned comparators are supplied to an ANDgate 1087, and the object pattern is discriminated as present when anoutput signal “1” is obtained from said AND gate.

(Embodiment 2-2)

FIG. 29 is a schematic view of a full-color copying machine employing anembodiment 2-2 of the present invention, wherein provided are an imagescanner unit 1201, and a full-color printer 1202 same as in theembodiment 2-1. An original illuminating halogen lamp 1205 and a firstmirror 1206 are included in a first original scanning unit 1298. Secondand third mirrors 1207, 1208 are included in a second original scanningunit 1299. In the original scanning operation, the first originalscanning unit 1298 is driven with a velocity V by unrepresented drivemeans, while the second original scanning unit 1299 is driven with avelocity V/2 in the same direction as that of the first originalscanning unit, by means of the unrepresented drive means, whereby thelight reflected from an original 1204 on the platen glass 1203 isfocused on a 3-line CCD sensor 1210 through a condenser lens 1209,maintaining always a constant optical distance, 1211 indicates a signalprocessing unit.

FIG. 28 is a schematic view around the condenser lens and the CCD sensorin said embodiment 2-2, which employs a 1:6 reduction optical system inthe image scanner unit 1201.

In FIG. 28, there is provided a 3-line sensor 1210 of which basicstructure is shown in FIG. 34. The lines respectively bear R, G and Bdyes evaporated thereon. Each pixel has a size of 10×10 μm, and thelines are separated by a distance of 180 μm. Said line distancecorresponds to a spatial aberration 1.08 mm on the original in the subscanning direction, so that, in the actual original reading operation,the signal processing unit 1211 delays the preceding R and G signals inthe sub scanning direction to match the B signal. A far infrared cut-offfilter 1301 has the same spectral characteristics as those of thedichroic mirror 1130 in the embodiment 2-1 shown in FIG. 17. A visiblecut-off filter 1302 and a near-infrared cutoff filter 1303 have thesubstantially same spectral characteristics as those of the filters1123, 1124 in the embodiment 2-1. Also, as in the embodiment 2-1, thefilter 1303 is provided with a focus correcting transparent glass plate1306 of a high refractive index. Said filters 1302, 1303 are mutuallyseparated by an angle 90° on a rotary shaft 1304, which is connected toan unrepresented stepping motor with a minimum rotation angle of 3.60°.Thus, said filters 1302, 1303 can be switched by rotating said steppingmotor by 25 pulses in a direction CW or CCW.

(Embodiment 2-3)

FIG. 31 is a schematic view around the lens and the CCD sensor of thefull-color image scanner employing a reduction optical system, wherein avisible cut-off filter 1322 for cutting off the visible light below awavelength 750 nm, and an infrared cut-off filter 1323 for cutting offthe light above a wavelength 750 nm, are positioned mutuallyperpendicularly about a rotary shaft 1324. Also a filter 1329, forcutting off the light above a wavelength 850 nm, and a glass plate 1326of a thickness of 2 mm for focus correction between the visible imagereading and the near-infrared image reading, are fixed on a rotary shaft1325. Said two rotary shafts 1324, 1325 respectively have pinions 1312,1313, and a linear movement of a rack 1311 connected to a solenoid 1310simultaneously switches the filters 1322, 1323 and the filters 1326,1329.

(Other Embodiments)

The foregoing embodiment employs a transparent dye capable of absorbingthe infrared light around 800 nm, but such dye is not limitative andthere may be employed any substance which is nearly transparent in thevisible region and is capable of absorbing the light of a specifiedwavelength range in the invisible region.

The switching between two filter systems can also be achieved by movingthe image reading sensor with respect to fixed filter means.

The optical filters are not limited to flat ones but may also be curved.

Also the correction for focus position in different wavelength regionsmay be achieved by a movement of the sensor or the lens.

Also the image reading sensor is not limited to the line sensor.

The foregoing embodiment employs a halogen lamp, but there may beemployed any light source capable of emitting the light in the visibleand near-infrared regions.

Also in the foregoing embodiment the standard white board is commonlyused for visible image reading and for infrared image reading, but theremay be employed separate standard boards respectively for both imagereadings.

The solid-state image reading device can be composed, in addition to thecharge-coupled device (CCD) explained above, of a MOS sensor or anamplifying device in which a capacitative load is connected to theemitter of a phototransistor, as disclosed in the U.S. Pat. No.4,791,469 awarded to the inventors T. Ohmi and N. Tanaka.

As explained in the foregoing, the embodiments allow to securely detectthe feature of the original with a simple structure.

(Embodiment 3-1)

FIG. 36 is a view of the apparatus constituting an embodiment 3-1 of thepresent invention, wherein provided are an image scanner unit 3201 forreading the original and effecting the digital signal processing, and aprinter unit 3202 for printing a full-color image on a sheet,corresponding to the original image read by the image scanner 3201.

The image scanner unit 3201 is provided with a pressure plate 3200. Anoriginal 3204 placed on a platen glass 3202 is illuminated by the lightcoming from a halogen lamp 3205 through an infrared cut-off filter 3208,and the reflected light from said original is guided by mirrors 3206,3207 and is focused by a lens 3209 onto a 4-line sensor (hereinaftercalled CCD) 3210, whereby the full-color information consisting of red(R), green (G) and blue (B) components and the infrared (IR) componentare supplied to a signal processing unit 3211.

A standard white board 5102 generates correction data for the data readby the R, G, B sensors 3210-2 to 3210-4.

A reference fluorescent plate 5103 is uniformly coated with fluorescentink showing fluorescent characteristics as shown in FIG. 42 andsubstantially same as those of the fluorescent information to bedetected, and is used for the correction of the output data of the IRsensor 3210-1.

The signal processing unit 3211 electrically processes the read signalsto separate the magenta (M), cyan (C), yellow (Y) and black (BK)components, for supply to the printer unit 3202. In each originalscanning operation in the image scanner unit 3201, one of the M, C, Yand BK components is plane sequentially supplied to the printer unit3202, whereby a printout is completed by four original scanningoperations in total.

The M, C, Y and BK image signals coming from the image scanner unit 3201are supplied to a laser driver 3212, which in response modulates asemiconductor laser 3213. The emitted laser beam is guided by a polygonmirror 3214, an f-θ lens 3215 and a mirror 3316 and scans aphotosensitive drum 3217.

A magenta developing unit 3219, a cyan developing unit 3220, a yellowdeveloping unit 3221 and a black developing unit 3222 in successiondevelop the electrostatic latent images of M, C, Y and BK colors withcorresponding toners.

A sheet supplied from a sheet cassette 3224 or 3225 is wound on atransfer drum 3223, and the toner images developed on the photosensitivedrum 3217 are transferred onto said sheet.

After the transfers of the four images of M, C, Y and BK colors insuccession, the sheet is discharged through a fixing unit 3226.

FIG. 37 shows the spectral characteristics of an infrared cut-off filter3208 positioned between the illuminating halogen lamp 3205 and theplaten glass 3203, and said filter cuts of the infrared component aboveabout 700 nm, within the spectral emission of the halogen lamp 3205shown in FIG. 38.

FIG. 39A shows the structure of the sensor 3210 (composed of CCD linesensors in the present embodiment).

There are provided a photosensor array 3210-1 for reading the infrared(IR) light, and photosensor arrays 3210-2, 3210-3, 3210-4 forrespectively reading the R, G and B light components.

Said four photosensor arrays of different optical characteristics areformed on a same silicon chip in monolithic manner, in mutually parallelarrangement in order to read a same line on the original.

Such configuration of the sensor allows to use the optical system, suchas the lens, commonly for the visible light reading and the infraredlight reading. It is thus rendered possible to improve the precision ofthe optical adjustment and to facilitate the operation thereof.

FIG. 39B is a magnified view of the photosensor elements, each having alength of 10 μm per pixel in the main scanning direction. Each sensorhas 5000 pixels in the main scanning direction, in order to read theshorter side (297 mm) of the A3-sized original with a resolving power of400 dpi. The R, G and B sensors are mutually separated by a distance of80 μm, corresponding to 8 lines for the sub scanning resolving power of400 lpi.

The IR line sensor 3210-1 and the R sensor 3210-2 are separated by adistance of 160 μm (16 lines) corresponding to the double of other linespacings. FIG. 40 shows the spectral sensitivities of this CCD, whereincurves 3261, 3262 respectively show the spectral characteristics of theCCD's for visible light and the CCD for IR light.

The R, G and B sensors 3210-2-3210-4 have apertures of 10 μm in the subscanning direction, but the IR sensor 3210-1 has a doubled aperture of20 μm, in consideration of a fact that said sensor reads the fluorescentlight of the IR light.

In general, the intensity of the fluorescent light is less than half,often about 10% or even less, of that of the exciting light. The presentembodiment secures the dynamic range of the infrared read signal byincreasing the light-receiving area per pixel, sacrificing the subscanning resolving power of the IR sensor.

In the present embodiment, the dynamic range of the read signal issecured by increasing the length of each pixel of the IR sensor in thesub scanning direction, but it is also possible to increase the lengthof each pixel in the main scanning direction, sacrificing the resolvingpower therein.

However, the above-mentioned difference in the size of the apertures maybe unnecessary if a sufficient dynamic range can be secured in theoutput of the IR sensor.

The line sensors are provided with optical filters thereon, in order toattain predetermined spectral characteristics in the IR, R, G and Bregions.

The spectral characteristics of the G, R and B line sensors will beexplained in the following, with reference to FIGS. 2 and 41.

FIG. 2 shows the characteristics of the conventional R, G and B filters,which also transmit the infrared light above the wavelength of 700 nm.For this reason, an infrared cut-off filter as shown in FIG. 41 hasconventionally been provided on the lens 209. In the present embodiment,however, the lens 209 cannot have such infrared cut-off filter, becausethe infrared component transmitted by said lens 209 is read by the IRsensor 3210-1.

In order to exclude the influence of said infrared light, the infraredcut-off filter is to be provided only between the R, G and B sensors andthe lens.

FIG. 3 shows the characteristics of a visible cut-off filter provided onthe IR sensor 3210-1. Said filter serves to eliminate the visible lightcomponent entering the IR sensor for reading the fluorescent componentof the IR region.

In the present embodiment there is conceived, as an example of the copyprohibited original, an original marked in a position (Xc, Yc) shown inFIG. 35 with ink having the above-explained fluorescent characteristics.

If the above-mentioned mark is detected in the infrared signal read fromthe original on the platen, the ordinary image forming operation isprohibited.

However the copy prohibited original is not limited, in size and in themarking, to that shown in FIG. 35.

FIG. 42 shows the reflective spectral characteristics of a recognitionmark contained in the copy prohibited original.

A curve 12201 indicates the synthesized spectral characteristics of thehalogen lamp 3205 and the infrared cut-off filter 3208 positionedbetween said lamp and the platen glass 3203. In the present embodiment,the copy prohibited original is recognized by utilizing, within saidspectral characteristics, an infrared component 12202 around 700 nm asthe exciting light and detecting infrared fluorescent light 12203 havingpeak at about 800 nm, coming from the recognition mark.

The present embodiment employs a halogen lamp as the originalilluminating lamp for simultaneously emitting at least the visible lightand the exciting light component for the infrared fluorescence, and thefilter 3208 is employed for preventing a wavelength component of theinfrared fluorescent from reaching the original.

In the present embodiment, the recognition mark is composed of asubstance capable of being excited by the infrared light and generatinginfrared fluorescence. For this reason said recognition mark can havearbitrary characteristics for the visible light. In the presentembodiment there is employed infrared fluorescent ink which issubstantially transparent to the visible light, so that the infraredfluorescent light can be detected without the recognition mark in thecopy prohibited original being noticed by the general public.

In the following, the principle of IR fluorescence reading will bebriefly explained. The original 3204 on the platen glass 3203 isilluminated by the light coming from the halogen lamp 3205 through theinfrared cut-off filter 3208. In general, the intensity of thefluorescence for example of 800 nm emitted from the recognition mark isweak, less than half, often about 10%, of that of the exciting light.

For this reason, within the light directly reflected from the original,longer wavelength components containing the wavelength component of theaforementioned infrared fluorescent light of 800 nm is eliminated by theinfrared cut-off filter 208, whereby the wavelength component of 800 nmentering the CCD is substantially composed of the fluorescent component.

As explained in the foregoing, the light illuminating the original ismade free of the spectral component of the fluorescent light generatedby said recognition mark and is made to sufficiently contain theaforementioned exciting light of 700 nm, whereby the S/N ratio of thefluorescent signal from the recognition mark can be improved.

The reflected light from the original is guided by mirrors 3206, 3207and is focused by a lens 3209 on the line sensors for reading the red(R), green (G), blue (B) and infrared (IR) components, in the CCD sensor3210.

Since the R, G and B line sensors 3210-2-3210-4 are provided with theinfrared cut-off filter for sufficiently attenuating the exciting lightof 700 nm as explained before, the full-color image reading can beachieved without the influence of said infrared exciting wavelength of700 nm and of the infrared fluorescent light.

Also the IR sensor 3210-1 is provided with a filter for cutting off thewavelength components below 700 nm as shown in FIG. 3, whereby it canonly read the infrared fluorescent component 12203 shown in FIG. 42.

These filters enable the extraction of the infrared fluorescent lightsimultaneously with the operation of reading and recording the originalimage, whereby the additional original scanning operation, such as thepre-scanning, required only for detecting the recognition mark by theinfrared fluorescent light, can be dispensed with.

The configuration explained above satisfactorily separates the ordinarycolor area and the infrared recognition mark area of the original.

(Embodiment 3-2)

The filter of the present invention may be provided in any positionbetween the lens and the CCD sensor, capable of separating the visiblelight beam and the infrared light beam. For example, it may be adheredto a cover glass of the CCD device as shown in FIG. 43, as a part of theCCD. Such structure improves the positional precision, and dispenseswith the positional adjustment of the compensating glass plate, therebyenabling to reduce the assembling time.

(Embodiment 3-3)

The filter of the present invention need not necessarily be composed ofa pigment or dye filter, but can be composed of a dichroic filterevaporated, as shown in FIG. 44, in a part of the cover glass where thevisible light beam passes.

(Embodiment 3-4)

All the foregoing embodiments employ a 4-line sensor of monolithicstructure. However, the present invention is applicable also to anequal-size optical system employing a short-focus lens array 12801 asshown in FIG. 46. In such case there may be employed a 2-line sensorconsisting, as shown in FIG. 45, of an RGB in-line sensor 12802-2 forvisible light reading and an IR sensor 12802-1 for infrared lightreading.

(Embodiment 3-5)

FIG. 47 shows the aberration (axial chromatic aberration) in the focusposition, depending on the wavelength, in the optical system employed inthe image reading system of the above-explained spectralcharacteristics.

As will be understood from FIG. 47, the optical system is usually sodesigned as to provide a satisfactory resolving power in the visibleregion, so that the focus position becomes aberrated in the infrared orultraviolet fluorescent region and the resolving power becomesdeteriorated. The correction of said deteriorated resolving power, ifmade by the lens itself, requires a significantly increased number oflens elements, inevitably resulting in undesirably low cost performance.For correcting said deterioration in the resolving power, therefore, aflat glass plate 12101 for correcting the focus position is insertedbetween the lens and the sensor for the visible light. Since thedifference in the focus position between the visible region and theinfrared region is about 0.4 mm as shown in FIG. 47, there can beemployed a correcting glass plate with a thickness of 1 to 1.5 mm. Inthis manner a desired resolving power can be obtained in the entirerange including the visible region and the infrared region.

(Embodiment 3-6)

The correcting glass plate of the present invention may be integrallyformed with the cover glass plate, utilizing plastic molding, as shownin FIG. 48. Such structure improves the precision of alignment, andenables cost reduction since the correcting glass plate is not composedof a separate part.

(Embodiment 3-7)

FIG. 49 shows the structure of the optical path splitting means and theoptical path length correcting means in the present embodiment, whereinprovided are a half mirror 3001-1 for splitting the optical path, and anordinary mirror 3001-2 with modified characteristics of the reflectingfilm for obtaining a high reflectance in the infrared region.

FIG. 51 shows the spectral reflectance of the mirrors 3001-1 and 3001-2.

FIG. 50 shows the configuration, after the light beams emerge from thelens, of a reading optical system employing the device of the presentembodiment. The light beam emerging from the lens is split into two bythe half mirror 3001-1 constituting a first plane of the device and thereflected light is focused on the visible light sensor, while thetransmitted light is reflected by the mirror 3001-2 constituting asecond plane, thereby being subjected to the correction of the opticalpath length, and is focused on the sensor for the IR light.

In this configuration, the difference L in the optical path lengthbetween the visible light and the infrared light is represented by:

L=2d(2n−1−n ² sin²θ)/n cos θ

while the distance y of separation between the visible light beam andthe infrared light beam is represented by:

y=2d tan²θ cos θ′ (sin θ′=n sin θ)

wherein d is the distance between the half mirror 3001-1 and the mirror3001-2, n is the refractive index of the material present between saidhalf mirror and said mirror, and θ is the incident angle of the lightbeam into the mirror. In the present embodiment, the desired value of Lis about 0.3 to 0.4 mm. For L=0.35 mm and refractive index n=1.51633,the distance d and the separation distance y are uniquely determined fora given value of the incident angle.

FIG. 53 shows the distance d and the separation distance y as a functionof the incident angle. As will be understood from FIG. 53, if theincident angle is selected in a range of 50° to 60°, the separationdistance y becomes 0.118-0.119 mm, so that the fluctuation in theseparation distance between the visible light beam and the infraredlight beam, resulting from the fluctuation in the incident angle, can besuppressed to the order of 1 μm. Also for a pixel size of 10 μm, theaberration from a multiple 120 μm of the pixel size (12 times in thiscase) becomes the order of 2 μm, so that the line interpolation of thevisible light beam and the infrared light beam can be satisfactorilyachieved.

As will be understood from FIG. 47, the optical system is usually sodesigned as to provide a satisfactory resolving power in the visibleregion, so that the focus position becomes aberrated in the infrared orultraviolet fluorescent region and the resolving power becomesdeteriorated. The correction of said deteriorated resolving power, ifmade by the lens itself, requires a significant increase in the numberof lens elements, inevitably resulting in undesirably low costperformance. For correcting said deterioration in the resolving power,therefore, the device 3001 for optical path splitting and for opticalpath length correction as shown in FIG. 50 is provided between the lensand the sensor. In this manner a desirable resolving power can beattained in the entire spectral range including the visible region andthe infrared region.

In this case, the distance of separation between the visible light beamand the infrared light beam is selected as an integral multiple of thepixel size of the aforementioned 4-line sensor. Among the three linesensors for the visible light, the spatial aberration in the subscanning direction is corrected by line delay elements as explainedbefore. If said distance of separation is so selected that the imagereading position of the line sensors subjected to said line delaybecomes equal to that of the line sensor not subjected to said linedelay, the line delay element can be dispensed with for the infraredsensor.

FIG. 52 shows the structure of a copying apparatus employing the presentembodiment. Said apparatus is different from the apparatus shown in FIG.36, in that the device 3001 is provided for the optical path lengthcorrection.

(Embodiment 3-8)

The foregoing embodiment employs a mirror having a high reflectance inthe infrared region, but, in the present embodiment, it is replaced by adichroic mirror capable of cutting off the visible light as shown in3210-1, whereby the CCD sensor for the IR light need not be providedwith the visible cut-off filter and can be prepared in a more simplemanner. Also, different from the pigment or dye filter to be provided onthe CCD sensor, the dichroic filter can arbitrarily select the visiblecut-off region, so that the precision of separation of the visible andinfrared lights can be improved.

(Embodiment 3-9)

The foregoing embodiments employ a half mirror for separating thevisible and infrared lights, but, in the present embodiment, it isreplaced by a dichroic filter of the characteristics shown in FIG. 54,whereby the light of the desired visible region only is guided byreflection to the CCD for visible image reading. As a result, the filterof said CCD sensor need not have the capability of cutting off theinfrared light as shown in FIG. 41 but can be composed of theconventional CCD filter so that the preparation of the CCD can besimplified.

(Embodiment 3-10)

The foregoing embodiment 3-7 employs a 4-line sensor of the monolithicstructure, but the same configuration may be applied to an equal-sizeoptical system employing a short-focus lens array as shown in FIG. 45.In this case, there is employed a 2-line sensor 12802 consisting of anRGB in-line sensor 12802-2 for visible light reading and an IR sensor12802-1 for IR light reading, as shown in FIG. 46. In case of such lensarray, the present invention is particularly effective, since thecorrection of the aberration in the focus position depending on thewavelength is almost impossible by an increase in the number of lenselements, as in the case of the reduction optical system but has to bemade in the improvement of the glass composition as it is composed of asingle lens.

As explained in the foregoing, the embodiments explained above of thepresent invention enable detection of the copy prohibited original,utilizing the detection of the infrared fluorescent ink which issubstantially transparent in the visible region, without influencing thepractical use in the visible light region.

Also satisfactory image reading can be realized without mixed presenceof information in the visible and infrared regions, by employingsuitable cut-off filters for excluding the light of other wavelengthregions in the signal for detecting the infrared fluorescent informationand in the signal for reading the visible information.

Also for the copy prohibited original, the ordinary copying operationcan be prohibited by recording information, not identifiable in thevisible light, in the form of visible information.

Also satisfactory image reading with a high resolving power can berealized in a wide spectral range including the visible and infraredregions, by providing means for correcting the focus positions of thesignal for detecting the infrared fluorescent information and the signalfor reading the visible information.

Also satisfactory image reading with a high resolving power can berealized in a wide spectral range including the visible and infraredregions, by providing means for satisfactorily separating the signal fordetecting the infrared fluorescent information and the signal forreading the visible information and correcting the focus positions ofsaid signals.

The solid-state image reading device may be composed, in addition to thecharge-coupled device (CCD) mentioned above, of a MOS sensor or anamplifying device in which a capacitative load is connected to theemitter of a phototransistor, as disclosed in the U.S. Pat. No.4,791,469 allowed to the inventors T. Ohmi and N. Tanaka.

As explained in the foregoing, the embodiments explained above enablessatisfactory reading of the light of the visible region and theinvisible region.

The photoelectric converting device of the present invention achievessatisfactory spectral sensitivity characteristics and satisfactoryresolving power, through the combination of a photoelectric convertingelement sensitive to the visible light and an infrared-visible lightconverting element.

The photoelectric converting element to be employed in the presentinvention is advantageously composed of an element absorbing the lightof the visible region and converting the same into an electrical signal.Examples of such element include a photovoltaic element such as aphotodiode, or a photoconductive element such as a phototransistor.

Also the infrared-visible light converting element to be employed in thepresent invention is preferably composed of an element utilizing:

1) infrared exhaustion effect;

2) multi-step energy transmission; or

3) infrared extinction effect.

The element utilizing the infrared exhaustion effect is to irradiate afluorescent material, excited to a semistable state by the irradiationof the light of a short wavelength, with infrared light therebygenerating the fluorescent light in the visible region. FIG. 57 shows anexample of the exciting spectrum, infrared exhausting spectrum and lightemission spectrum.

Such element is preferably composed of a fluorescent material such asZnS or SrS doped with a transient metal.

The irradiation of the short-wavelength exciting light may be conductedbetween the sequence of image reading or simultaneously with theirradiation of the infrared light, but a filter is preferably used, inorder that said short-wavelength exciting light does not enter thephotocell part.

The element for effecting infrared-visible conversion by multi-stepenergy transmission preferably employs a material such as NaWO₄ dopedwith Yb³⁺, Y_(0.84)Yb_(0.15)Er_(0.01)F₃, NaY_(0.69)Yb_(0.30)Er_(0.01)F₄,BaY_(1.34)Yb_(0.60)Er_(0.60)F₈, Y_(0.74)Yb_(0.25)Er_(0.01)OCl orY_(0.65)Yb_(0.35)Tm_(0.001)F₃, and these materials generate visiblelight by the energy transmission in two or three steps from Yb³⁺ to thelight emission center.

The element utilizing the infrared extinction effect relies on aphenomenon, when a fluorescent material excited with a fluorescent lampfor example of neat-ultraviolet region is irradiated with infraredlight, the light emission is extinguished in the irradiated portion.Such element is preferably composed of ZnS doped with CuAl.

(Embodiment)

FIG. 55 is a schematic cross-sectional view of a CCD image sensoremploying an embodiment of the photoelectric converting element of thepresent invention.

In a P−Si silicon substrate 4101, a photocell area 4102 having an n⁻ Siarea is formed as the photoelectric converting element. Thephotocarriers 4122 generated by the incident light 4112 are collected inthe photocell 4102, then transferred by a polysilicon electrode 4106 ofthe accumulation unit, a polysilicon electrode 4107 of the transferunit, and polysilicon electrodes 4108, 4109 of the buried-channel CCDregister unit, and taken out as an output signal from an output gate.

Each pixel is isolated by a P⁺ Si channel stopper 4111 and a field oxidelayer 4110.

In order to avoid light entry except for the photocell, aluminumlight-intercepting layers 4103, 4103′ are doubly provided, utilizinginsulation layers 4104, 4104′ whereby the incident light 4112 onlyenters an aperture 4114 in which an infrared-visible light convertingelement 4105 is provided.

Consequently the incident light 4112 is converted, by said element 4105,into the light of a wavelength in the visible region, and thus convertedlight is converted into the carriers, by the photocell 4102 havingsatisfactory sensitivity for the visible light. Such photocell 4102 hasbeen developed for many years and, since the photocell structure for thevisible light can be employed, the complex photocell structure for theinfrared light is not required.

In the image reading device shown in FIG. 55, with the aperture 4114 ofa size of 13 μm and irradiated with the light of 800 nm, utilizing theIR Phosphor Plate consisting of Mn-doped SrS and prepared by EastmanKodak Co. as the infrared-visible light converting element, there wasobtained a signal intensity ratio as high as 50 dB in comparison withthe adjacent pixel completely shielded from the light.

A similar measurement when said infraredvisible light converting elementwas replaced by a known visible cut-off filter provided an insufficientsignal intensity ratio of 20 dB to the adjacent pixel, and the outputwas as low as ½ of the output when the infrared-visible light convertingelement was employed.

FIG. 56 shows an example of the image reading device utilizing thephotoelectric converting element of the present invention, applied to afull-color image reading.

On photocells 4208 there are provided wavelength selecting filters,consisting of a blue transmitting filter 4201, a green transmittingfilter 4202 and a red transmitting filter 4203, by means of which thevisible optical signals are read. Also the photoelectric conversion byway of infrared light-visible light-carriers is achieved by thecombination of an element 4204 composed of an infrared-visible lightconverting material and a photocell 4208′ provided thereunder and havingsensitivity to the visible light.

Since such photocells 4208, 4208′ can be prepared with a same materialin a same process, they are advantageously employed in the image sensorconsisting of integrated semiconductor circuits, for effecting thedetection in the visible and invisible regions.

FIG. 58 shows an example utilizing the infrared extinction effect.

A fluorescent lamp 4416 emits the exciting light 4417 to generatefluorescent light from an infrared-visible light converting element 4405consisting of an infrared extinction material, into which the infraredlight 4412 enters to extinguish the fluorescent light in the irradiatedposition. A filter 4415 only transmits the light generated by saidinfrared-visible light converting element 4405, thus introducing thefluorescent light into a photocell 4418. In response to the entry of theinfrared light 4412, the fluorescent light is extinguished, whereby thephotocell 4418 no longer receives the incident light and thephotocarriers are no longer generated.

As explained in the foregoing, the use of an infrared-visible convertingelement in the photoelectric converting device provides satisfactorysensitivity and excellent resolving power even in the detection of theinfrared optical signal.

What is claimed is:
 1. An image reading device for reading visibleinformation and invisible information on an original, said image readingdevice comprising: a monolithic solid-state image sensor prepared on asubstrate, said monolithic solid-state image sensor including a sensorfor reading visible information, wherein the visible and invisibleinformation are focused on said monolithic solid-state image sensor; anda filter for intercepting invisible light provided between the sensorfor reading visible information and the original, wherein said filter isa glass filter adhered to a cover glass on said monolithic solid-stateimage sensor and is inserted between the sensor for reading visibleinformation and a lens, and wherein the invisible information isinformation based on fluorescent light.
 2. An image reading device forreading visible information and invisible information on an original,said image reading device comprising: a monolithic solid-state imagesensor prepared on a substrate, said monolithic solid-state image sensorincluding a sensor for reading visible information, wherein the visibleand invisible information are focused on said monolithic solid-stateimage sensor; and a filter for intercepting invisible light providedbetween the sensor for reading visible information and the original,wherein said filter is a dichroic filter evaporated on a cover glass onsaid monolithic solid-state image sensor and is inserted between thesensor for reading visible information and a lens, and wherein theinvisible information is information based on fluorescent light.